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Preventing pressure spikes with vented housing

04 Dec 2015  | Thilo Haiss

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Electronics in electric cars, hybrid cars, or even the ones with conventional combustion engines are exposed to constant pressure fluctuations. Yet driving is not the only activity that poses major challenges for electronics housings. Shutting off the engine in particular causes huge pressure spikes, putting considerable stress on the seals that are supposed to protect sensitive electronics from dirt and liquids.

When the vehicle is in operation, the wind cools the electronics that heat up in the engine compartment. However, if the car is sitting in traffic or at a traffic light, then this natural coolant disappears. As a result, the temperature under the hood quickly shoots up. This increase is even more serious when the car remains stationary for several hours. The heat from the engine rapidly drives up the temperature, which in turn produces pressure spikes in the electronics housings. Because these spikes equalise only very slowly without vents, enormous strain is put on the seals. This scenario happens at least twice a day in commuter cars; the recurring stress can weaken the seals over time, eventually allowing ingress of dirt particles and liquids into the housing's interior. Ultimately, this can damage the sensitive electronics.

Figure: Commuter test: dangerous pressure spikes are par for the course.

Gore's vent specialists tested the temperature and pressure changes in two identical electronics housings installed under the hood. One electronics housing remained in its original condition (in other words, non-vented), while a GORE Automotive Vent was integrated into the other one. The test observed both electronics housings during a typical "commuter day" – starting at 4 p.m. with the drive home and concluding with the drive back to work the next morning (figure).

Temperature and pressure spikes in non-vented housings ...
While the driver was running afternoon errands, the wind caused by the car's motion was able to cool off the engine sufficiently. Yet around 5:30 p.m., when the car was sitting in rush hour traffic, the temperature under the hood rose from roughly 15°C to about 45°C (yellow line). It didn't drop until traffic started moving and the generated breeze began cooling the electronics again – and even then it fell only slightly. As soon as the car was back at home, with the engine turned off and no wind to dissipate the heat, the temperature climbed up to a new high of nearly 60°C. There it remained until hours later, when the cool night air brought it back down.

In the non-vented housing, this temperature increase created a positive pressure of 150 mbar (red line). Positive pressure of just 70 mbar over an extended period of time can already be dangerous, as it allows the seal to become porous. It wasn't until the engine cooled off several hours later that the pressure gradually fell to its original value of 0 mbar. In winter, if the car is exposed to outside temperatures of just above freezing for an entire night, negative pressure forms in the non vented housing, putting critical strain on the seals. As a result, water and dirt particles can penetrate the housing.

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